To conserve nickel and reduce costs, a number of procedures have been adopted by the nickel plating industry. Some of these procedures include reducing the thickness of nickel deposited, substituting cobalt for some or all of the nickel when cobalt is less expensive or more readily available, and more recently electrodepositing nickel-iron, cobalt-iron, or nickel-cobalt-iron alloys in which as much as 60% of the deposit may consist of relatively inexpensive iron. However, when deposit thickness is reduced, it is necessary to use more effective or "powerful" nickel brighteners or higher concentrations of nickel brighteners, so that the degree of brightening and leveling to which the nickel plating industry has grown accustomed may be obtained. The more "powerful" nickel brighteners or high concentrations of brighteners, while capable of producing the desired brightening and leveling, may nevertheless cause unacceptable side effects. The nickel deposits may peel or may be highly stressed, severely embrittled, less receptive to subsequent chromium deposits or exhibit hazes, reduced low current density covering power or "throw" or striations and skip plate, i.e., areas in which a deposit is not obtained.
Although in many respects, the electrodeposition of nickel-iron, cobalt-iron or nickel-cobalt-iron alloys is very similar to the electrodeposition of nickel in that similar equipment and operating conditions are employed; nevertheless, electroplating with iron containing alloys of nickel and/or cobalt presents some special problems. For example, one requirement in the electrodeposition of iron alloys of nickel and/or cobalt is that the iron in the electroplating solution should be predominantly in the ferrous state rather than the ferric. At a pH of about 3.5, basic ferric salts precipitate and can clog the anode bags and filters and may produce rough electrodeposits. It is, therefore, advantageous to prevent any ferric basic salts from precipitating. This can be accomplished by the addition of suitable complexing, chelating, anti-oxidant or reducing agents to the iron containing electroplating alloy bath as taught by Koretzky in U.S. Pat. No. 3,354,059; Passal in U.S. Pat. No. 3,804,726; or Clauss et al in U.S. Pat. No. 3,806,429. While these complexing or chelating agents are necessary in order to provide a solution to the ferric iron problem, their use may also result in several undesirable side effects. They can cause a reduction in deposit leveling and can also produce striated, hazy or dull deposits which may further exhibit step plate or even skip plate, i.e., areas which are not plated, or else plated only very thinly compared to other sections of the deposits.
In order to overcome the deleterious effects of high concentrations of brighteners or "powerful" brighteners, or to counteract the undesirable side effects of iron or iron solubilizing substances when these are present in nickel and/or cobalt, or iron containing nickel and/or cobalt electroplating baths, the addition of various sulfinic acids or their salts has been recommended by Brown in U.S. Pat. No. 2,654,703. Unfortunately, the sulfinic acids and their salts are unstable and subject to rapid oxidation by the oxygen of the atmosphere to the corresponding sulfonic acids or sulfonate salts, in which state they are no longer efficatious in overcoming the various side effects mentioned above. The use of sulfinic acids or their salts also severely reduces deposit leveling.
It is an object of this invention to provide processes and compositions for depositing electrodeposits of nickel, cobalt, or binary or ternary alloys of the metals selected from nickel, cobalt and iron which possess a greater tolerance for high concentrations of brighteners. It is a further object of this invention to provide deposits of nickel, cobalt or binary or ternary alloys of the metals selected from nickel, cobalt and iron characterized by increased ductility, brightness, covering power, and leveling or scratch hiding ability. If is a further object of this invention to overcome the problems caused by the presence of iron or iron solubilizing materials in iron alloy electroplating baths of nickel and/or cobalt. Other objects of this invention will be apparent from the following detailed description of this invention.